This invention relates to gas insulated transmission lines in which an inner conductor is provided in segments with a joint assembly permitting relative movement of the segments.
Reference is made to Bolin U.S. Pat. No. 4,111,511, Sept. 5, 1978 on a high current contact assembly for gas insulated transmission lines. The Bolin patent discloses a contact assembly for electrically connecting two conductors wherein a plug member is secured to one conductor segment and a socket member is secured to another conductor segment with the plug being received by the socket member. Within an annular recess of the socket member a plurality of contact fingers are disposed in a holder that has an axial projection extending therefrom adjacent the contact fingers and radially outward therefrom. Resilient biasing means are disposed between the contact fingers and the holder and act upon the contact fingers and loading means are utilized to produce a force upon the contact fingers. The contact fingers thus provide good electrical contact between the plug and socket while allowing relative movement of those members. The description of the Bolin patent is herein incorporated by reference.
In accordance with the preferred embodiment of the above-mentioned patent the plug member fits inside the end of the conductor segment to which it is welded by a filet weld. Also, the socket member is welded to the extremity of the conductor segment to which it is bonded. In that embodiment, an electrical shield extends over the parts of the joint assembly including the contact fingers and the joint between the plug member and its conductor segment although not the weld between the socket member and its conductor segment. The shield is a metal element that is provided in electrical contact with the plug by a spring bias contact through one or more apertures within the conductor segment to which the plug is joined.
Additionally, the preferred embodiment of the above-mentioned patent provides for mounting the contact fingers by an annular retainer, a holding ring and bearing members which entail a weld between the retaining member and the socket member.
Assemblies as taught by the above-mentioned patent have been made and used successfully. However, the thrust of development at the present time is to provide gas insulated transmission lines of greater simplicity in terms of numbers of parts, less expensive parts, and easier fabrication and assembly without giving up anything in terms of performance capability. It is primarily to achieve such qualities in a shielded joint assembly that the present invention is directed.
Reference is also made to Meyer et al. U.S. Pat. No. 4,038,486, July 26, 1977, which is directed to a joint assembly used in conjunction with a nearby supporting insulator assembly.
Electrical joints in gas-insulated transmission lines must be of a smooth electrical shape to prevent dielectric breakdown from the joint, at the high voltage of the central conductor, to the outer conductor which is at ground potential. They must also carry high currents without generating so much heat that there is impaired operation and must allow for axial relative motion in a sliding contact arrangement because of thermal differences from one end of the transmission line to the other. In addition, the joint must allow for some degree of bending at the joint, provide mechanical support radially and control the movement of conductive particles that may be generated during joint operation as a result of the sliding and bending movements. A joint assembly in accordance with the present invention achieves these requirements with relatively few, simple parts and allows for rapid assembly during manufacture or under field conditions.
In accordance with the invention, briefly, plug and socket ends are respectively welded to the major portions of two inner conductor segments with the plug shaped at the weld end to allow minimal weld fixturing and so that it can easily be sized for any particular conductor inner diameter. In particular, the plug end has an inner portion that fits within the adjacent major portion of the inner conductor segment, and an intermediate portion having an outer diameter substantially equal to that of the conductor segment major portion with the plug inner and intermediate portions forming a shoulder or stop against which the major portion of the inner conductor segment abuts to fix the location of the parts during welding. The outer portion of the plug end is configured with an outer diameter less than the inner diameter of the socket end within which it fits.
A contact means similar to that of the above-referred to Bolin patent is utilized except that the contact means is assembled to the socket member simply by having an end load design and the retaining is accomplished using a retaining ring to allow rapid assembly and/or replacement. The ring is simply a split ring of metal fitting within a slot in the surface of the socket. Its use is effective to hold the contacts and is beneficial in avoiding the need for any weld.
The shield is a machined or spun metal member that has spring loaded contacts (one or more), to retain the shield to the plug and to electrically connect them together. The shield covers the welds for both the plug and socket ends and the contact area. This allows both the welds to be merely rough-finished. Alternatively, where the shield is desired to be made shorter, the weld for the socket end need not be covered by the shield but it is then smooth finished.
Additional features include the provision of the permanently tacky material coated on the mid inside diameter region of the shield in order to trap any particles generated by contact wear or not removed in the manufacturing process. Furthermore, a plastic guide ring is installed inside one end to prevent particle generation and to act as a secondary particle barrier.
The various features of the invention, preferably used in combination, provide the needed functions of voltage shielding, current transfer, flexibility, axial motion and particle control in a compact and economical design.